ImdsV2: Throw on MTLS when OS is not Windows

src/client/Microsoft.Identity.Client/ApiConfig/AcquireTokenForClientParameterBuilder.cs

@@ -4,9 +4,6 @@
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
-using System.Security.Cryptography;
-using System.Security.Cryptography.X509Certificates;
-using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.Identity.Client.ApiConfig.Executors;
@@ -15,10 +12,9 @@
 using Microsoft.Identity.Client.Extensibility;
 using Microsoft.Identity.Client.Internal;
 using Microsoft.Identity.Client.Internal.ClientCredential;
-using Microsoft.Identity.Client.ManagedIdentity.V2;
 using Microsoft.Identity.Client.OAuth2;
+using Microsoft.Identity.Client.PlatformsCommon.Shared;
 using Microsoft.Identity.Client.TelemetryCore.Internal.Events;
-using Microsoft.Identity.Client.Utils;
 
 namespace Microsoft.Identity.Client
 {
@@ -100,14 +96,25 @@ public AcquireTokenForClientParameterBuilder WithSendX5C(bool withSendX5C)
         /// <returns>The current instance of <see cref="AcquireTokenForClientParameterBuilder"/> to enable method chaining.</returns>
         public AcquireTokenForClientParameterBuilder WithMtlsProofOfPossession()
         {
-#if NET462
             if (ServiceBundle.Config.IsManagedIdentity)
             {
-                throw new MsalClientException(
-                    MsalError.MtlsNotSupportedForManagedIdentity,
-                    MsalErrorMessage.MtlsNotSupportedForManagedIdentityMessage);
-            }
+                void MtlsNotSupportedForManagedIdentity(string message)
+                {
+                    throw new MsalClientException(
+                        MsalError.MtlsNotSupportedForManagedIdentity,
+                        message);
+                }
+
+                if (!DesktopOsHelper.IsWindows())
+                {
+                    MtlsNotSupportedForManagedIdentity(MsalErrorMessage.MtlsNotSupportedForNonWindowsMessage);
+                }
+
+#if NET462
+                MtlsNotSupportedForManagedIdentity(MsalErrorMessage.MtlsNotSupportedForManagedIdentityMessage);
 #endif
+            }
+
             if (ServiceBundle.Config.ClientCredential is CertificateClientCredential certificateCredential)
             {
                 if (certificateCredential.Certificate == null)

src/client/Microsoft.Identity.Client/MsalErrorMessage.cs

@@ -442,6 +442,7 @@ public static string InvalidTokenProviderResponseValue(string invalidValueName)
         public const string MtlsInvalidAuthorityTypeMessage = "mTLS PoP is only supported for AAD authority type. See https://aka.ms/msal-net-pop for details.";
         public const string MtlsNonTenantedAuthorityNotAllowedMessage = "mTLS authentication requires a tenanted authority. Using 'common', 'organizations', or similar non-tenanted authorities is not allowed. Please provide an authority with a specific tenant ID (e.g., 'https://login.microsoftonline.com/{tenantId}'). See https://aka.ms/msal-net-pop for details.";
         public const string MtlsNotSupportedForManagedIdentityMessage = "IMDSv2 flow is not supported on .NET Framework 4.6.2. Cryptographic operations required for managed identity authentication are unavailable on this platform.";
+        public const string MtlsNotSupportedForNonWindowsMessage = "mTLS PoP with Managed Identity is not supported on this OS. See https://aka.ms/msal-net-pop.";
         public const string RegionRequiredForMtlsPopMessage = "Regional auto-detect failed. mTLS Proof-of-Possession requires a region to be specified, as there is no global endpoint for mTLS. See https://aka.ms/msal-net-pop for details.";
         public const string ForceRefreshAndTokenHasNotCompatible = "Cannot specify ForceRefresh and AccessTokenSha256ToRefresh in the same request.";
         public const string RequestTimeOut = "Request to the endpoint timed out.";